Iron-based and nickel-based superalloys are widely used to form certain components of gas turbine engines, and other turbine engines, including structural components, combustors and turbine airfoils such as vanes and blades. While high-temperature superalloy components are often formed by casting, circumstances exist where superalloy components are preferably fabricated or are required to be fabricated by welding separate assemblies. For example, components having complex configurations, such as turbine midframes and shroud support rings, can be more readily fabricated by welding separate cast or wrought forms together. Therefore, it is often more practical and cost effective to fabricate complex components by welding together individual assemblies rather than casting or forging the component as a unitary article. The welding procedures are very labor intensive, time consuming, and expensive, particularly when the pre-weld solution process required to prepare the article for welding must be performed in a vacuum.
GTA welding processes are generally often used to weld nickel-based and iron-based superalloy assemblies. The wide weld area causes significant distortion and a relatively large heat affected zone volume.
Recent advancements in penetration enhancement technology for flux-assisted GTA welding have produced a flux material that permits the use of gas tungsten arc (GTA) welds to join material thickness greater than about 0.1 inch in a single pass with a square butt preparation; this processing has been used in place of electron beam (EB) welding for nickel-base and iron-base superalloys. In addition, the same processing has been used to weld thinner sections but with significantly reduced heat input as compared with conventional GTA processing. A proprietary weld flux has recently been created, known as FASTIG SS-7™, which is owned by Edison Welding Institute, comprising blended solid powders mixed into a carrier such as methyl ethyl ketone (MEK), such blended powders comprising NiO, Ti2O3, TiO2, TiO and a manganese silicate compound. FASTIG SS-7™ contains a plurality of different metal oxides and is applied to the face side of articles to be welded in the form of a paste. When the flux is applied to the face side of nickel-base or iron-base superalloy substrates and a GTA process is used to weld the substrates, a much deeper and narrower weld is created than is normally created with a GTA process. However, the use of a flux such as FASTIG SS-7™ is tedious to apply and adds additional product costs to the superalloy substrate welding process. In addition, when a flux such as FASTIG SS-7™ is used, the flux may accidentally be applied to the faying surfaces, which causes the GTA process to fail.
There is accordingly a need for an improved technique for welding articles made of nickel-base and iron-based superalloys. The present invention fulfills this need, and further provides related advantages.